The influence of Yellow-sand (KOSA) on the forest, the presumption of the sulfur sources identification and the contribution rate of dry deposition

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In this research, it aims to evaluate the influence of Yellow-sand (KOSA) on the forest, to identify sulfur sources of SO_4^<2-> of rainwater (precipitation, thoughfall, stemflow) by the sulfur isotopic method, and to estimate contribution rate of dry deposition on total deposition.The outline of the result at all periods is as follows.We investigated qualitative change of rainwater in an evergreen broadleaved forest in a southern part of Japan1. KOSA flies from a continental desert to Japan at the early spring. Observation frequency of KOSA is an increasing tendency for the long term. In the spring of 2002 when the especially maximum KOSA in Beijing was observed, the color of aerosol filter presented yellowish. The Ca^<2+> concentration of the aerosol at KOSA event became 20-70nmol/m^3, and was higher than these values (20 nmol/m^3 or less) at normal event. The ion concentrations in precipitation, thoughfall and stemflow at KOSA event were higher than these at normal event. The influe … More nce on the forest by KOSA was admitted.2. The sulfate concentration and sulfur isotopic ratio of the wet deposition at 20 precipitation events and the dry deposition at 9 precipitation events were determined. The SO_4^<2-> concentrations increased in the order of precipitation, throughfall and stemflow, whereas their sulfur isotopic ratio( δ^<34>S) decreased in the order of precipitation, throughfall and stemflow. These results suggest that δ^<34>S-depleted light sulfur is added to throughfall and stemflow. On the other hand, δ^<34>S values of aerosol and gas were +2.7〜+5.3‰ and-2.1〜2.0‰, respectively. The latter is light enough to reduce the δ^<34>S values of throughfall and stemflow. Therefore we concluded that 1) SO_2 in dry deposition is the main substance causing low pH of stemflow and throughfall, 2) a lot of SO_4^<2-> with light δ^<34>S value are loaded to precipitation flowing down as stemflow and throughfall.3. About 60 percent of total deposition (wet deposition and dry deposition) was loaded to the forest by a dry deposition, using the mass balance model. Less